Rectifier for alternating currents.



No. 879,061. PATENTED FEB. 11,1908. G. w. PIERCE. RECTIFIER FORALTERNATING OURRENTS.

APPLICATION FILED JAN.11, 1907.

Jul/19min):

been properly calibrated.

the electromotive force is in the other dire-c- UNITED STATES PATENTOFFICE.

GEORGE W. PIERCE, 'OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TOMASSACHUSETTS '..WIRELESS EQUIPMENT COMPANY, OF BOSTON, MASSACHUSETTS, ACORPORATION OF NEW YORK.

RECTIFIER FOR ALTERNATING CURRENTS.

Specification of Letters Patent.

Patented Feb. 11, 1908.

Application filed January III 1907. Serial No. 351,773.

To all whom it may concern:

Be it known that I, GEORGE W. PIERCE, a citizen of the United States,and resident of Cambridge,Massachusetts,Middlesexcounty, have inventedcertain new and useful Improvements in Rectifiers for AlternatingCurrents, of which the following is a specification.

My invention relates to rectification of alternating currents or inother words to means for obtaining a direct current from an alternatingcurrent. I

The current obtained may be truly continuous or it may be intermittentin character but it is direct in the sense that it may be used tooperatedirect-current machinery, will deflect a permanent magnet and bedeflected thereby and may be measured by instruments such as are usedformeasuring direct currents when such instruments have In practicing myinvention I rectify currents from alternating sources by means of asubstance which in some way not at present clearly understood permits agreater current to pass through it when the impressed electromotiveforce is in one direction than when tion. I have discovered that certainsolid substances among which are carb'orundum, molybdonite, hessite,octahedrite, brookite, hematite, coovellite, possess this property ofunilateral conductivity. Pyrolusite and psylomelan also possess thisproperty. There are also a number of mineral oxids and sulfids of metalswhich have this property to a greater or less extent and some of theseminerals might be successfully used as a permanent and reliablerectifier in electrical apparatus.

Carborundum possesses the property of unilateral conductivity to amarked extent and may be used with advantage as a rectifier foralternating currents especially in cases where permanence and uniformityof action are of importance or are essential. I therefore prefer toemploy carborundum in practicing my invention although other solidspossessing the property of unilateral conductivity to the requisitedegree may be utilized.

In rectifying alternating currents by a solid which is unilaterallyconductive the] electrical connections with the rectifier may be made bylacing the solid in a metallic clamp, by p ating or coating parts withmeta and connecting conductors thereto, or in any other suitable manner.The rectifier is put in electrical connection with the instrument ormachine to be used and in connection with the alternating current leads.The connection may be a series or parallel connection and maybe eitherdirect or inductive.

For some purposes it may be found desirable to use a direct current orelectromotive force superposed upon the rectifier inaddition to thealternating current or electromotive force. these solid rectifiers, andespecially carborundum permanently retain the property of unilateralconductivity, and that the rectifying action is permanently uniform orpractically so. I havealso found that by reason of these properties I amenabled to combine the rectifying solid with other devices in producinginstruments for measuring currents and voltage from alternating sourceswhich are free from the well-known disadvantages and limitations of thealternating current measuring instruments as commonly constructed, andwhich are equal in precision and efficiency to direct current measuringinstruments. The combinations and features by which such instruments areprovided constitute important features of my invention. For the purposeof illustration I have shown diagrammatically in the accompanyingdrawings several forms of apparatus or instruments embodying myinvention.

In these drawingsFigure 1 is a diagrammatic view of an apparatus orinstrument which may be used for mesauring the current in'an alternatingcircuit. Fig. 2 is a similar view of a different form of apparatus orinstrument which may be used for the same purpose; and Fig. 3 is asimilar view of a.

difierent form of apparatus or instrument which is especially designedfor measuring small alternating currents such for instance as areemployed in telephony.

In the apparatus or instrument shown in Fig. 1 the rectifying meansconsists of a piece A of unilaterally conductive solid preferably one ormore crystals of carborundum which binding posts G and D.

nected through is held in a metallic clamp. The jaws B B of the clampare insulated from each other and the jaw B is movable so that it may beadjusted in securing the rectifying solid A in place. The jaw B isconnected through a conductor 0 with a binding post D and the other jawBis connected through a conductor E with a device operable by directcurrents. This device in the instrument shown is of substantially thesame construction as the indicating mechanism of well knowndirectcurrent ammeters or voltmeters. The indicating device consists ofa permanent magnet F provided with pole pieces F between which a coil Fis mounted. The coil F is mounted .to turn upon suitable pivots notshown and is yieldingly held in normal position by mean of light springs(not shown) in a well known manner. Connected with the coil F is anindicating pointer or finger F which 00-: The coil F is conoperates witha scale F.

the conducting wire E with the rectifier and through the'conductor Ewith a binding post G. The binding posts G and D are connected by aresistance H through which the greater part of the current passingthrough the leads I I passes. In using the instrument which is designedfor measuring currents, alternating source are connected with the Acertain proportion of the current passes through the circuit leadingfrom binding post D to the binding 0st G for instance. This current isrectified y the rectifier A so that a greater current flows in onedirection through the circuit than through the other, the effect beingthe same as if a current equal to the diflerence in these twocurrentsfflowed in one direction through the circuit. When this currentflows through the coil F the coil is deflected to acertain degreedepending u on the amount of current. By properly ca ibrating theindicating devices the pointer F may be made to indicate the amount ofcurrent passing over the leads I I upon the scale F The resistance H notonly acts as a shunt for a greater part of the current, but also by itscooperation with the rectifier A it prevents a uivering or oscillatingof the pointer when de ected. The reason for this is that when .thecurrent is in one direction the rectifier offers comparatively littleresistance to the flow of the current, and considerable current passesthrough the coil of the indicating devices deflecting the pointer. Whenthe current is in the opposite direction, however, the rectifier offersa high resistance to the flow of the current, and practically all thecurrent goes through the shunt H. The pointer therefore remainspractically at rest at the point to which it has been deflected.

I have found that the resistance of the unilaterally conductive solidsuch as carborundum decreases with an increase in the the leads I I froman current passing through it and in order that I the divisions on thescale F may be substantially e ual throughout the scale or the smallerdivisions be located as desired, I prefer to introduce a resistance J inthe circuit of the measuring instrument. 1 By properly proportioningthis resistance to the resistance of the circuit the deflections of theneedle may be such for different currents that the divisions of thescale may be made substantially equal or distributed as desiredthroughout the length of the scale. The resistance J also acts or mayact to counteract any slight variations in the resistance offered by therectifier to the passage of the current due to changes in temperature.Carborundum, for"instance',--has a negative temperature coefficient,while the resistance has a positive temperature coefficient. That is tosay, the resistance of the carborundum decreases with the increase oftemperature, while the resistance of the resistance coil J increaseswith the increase of temperature. By properly proportioning theresistance, therefore, it may be made to substantially counteract anyvariations in the rectifier due to temperature changes. While thevariations due to temperature" changes may not be sufficient under manyconditions to require elimination, their elimination may be important indelicate instruments for making very fine and accurate measurements, andare desirable in any case. In the case of delicate instruments formaking accurate measurements, it is preferred to construct theresistance J of metal having a high tem erature coefficient.

T e range of the instrument may be increased by roviding two or moreresistances H either of which may be brought into the circuit in whichcase two scales will be pro vided as is usual in direct currentmeasuring instruments.

An instrument having substantially the construction indicated in Fig. 1but with the resistance I-I omitted or made of high value and properlycalibrated may be used as a volt-meter.

In the apparatus shown in Fig. 2 the same construction of indicatingdevices are shown as are shown in Fig. 1 and this instrument as shown isalso designed for measuring currents. In this construction therectifying solid A and the, indicating devices are connected in parallelinstead of in series as in Fig. 1. In other respects the construction issubstantially the same as the construction indicated in Fig. 1. When'theinstrument indicated in this figure is connected with the leads I I froman alternating source, part of the current in the circuit between thebinding posts G and D passes through the rectifying device and a partthrough the indicating instrument. Since more of the current passesthrough the rectifying device in one direc-' 1:

- a series connection.

tion than in the other a greater current will flow through theindicating device in one direction than in the other and the result willbe a rectified or substantially direct current passing through theinstrument. In this case the resistance J may be introduced in thecircuitfor the same purpose for which it is introduced in the circuit inthe construction of Fig. 1.

The instrument illustrated in Fig. 2 like the instrument illustrated inFig. 1 may be used as a volt-meter by omitting the resist ance H andproperly calibrating the instrument so that the pointer and scale willindicate the difference in )otential between the binding posts G andwhen these binding posts are connected with the leads from analternating source.

In Fig. 3 an instrument is illustrated in which the circuit of therectifying device and indicating devices are inductively connected withthe circuit to be investigated. In this construction the leads I I fromthe alternating source are connected with the binding posts G D andthese binding posts are connected with opposite ends of the primary coilK of an induction coil. coil K of the induction coil is in connectionwith the indicating devices and rectifier, the connection in theinstrument indicated being As shown one end of the secondary coil K isconnected through a wire L with the coil F of the indicating device andthe other end of the secondary coil is connected throu h a connectingwire M of a resistance M with the jaw B of the clamp which holds therectifying solid A. The other jaw B of the clamp is connected through aconductor N with the coil F.

In using this instrument the alternating current through the primary Kof the induction coil induces alternating currents in the secondary Kwhich are rectified by the rectifying device A so that the indicatingdevices are operated to indicate either the current or voltage of thecircuit being investigated accordin to the calibration of theinstrument.

In ilustrating and explaining the various features of the invention noattempt has been made to indicate or describe the specific constructionand arrangement of the parts referred to as such construction andarrangement is not deemed essential and maybe whatever is best suited tothe conditions under which the apparatus in which the invention isembodied is to be used.

Without attempting to point out the various constructions andarrangements in which The secondary what I claim and desire to secure byLetters Patent is 1. In an electrical apparatus, a rectifier foralternating currents consisting of carborundum.

2. An electrical measuring instrument comprising a unilaterallyconductive solid, calibrated indicating devices operable by small directcurrents in electrical connection therewith, and means for electricallyconnecting a source of alternating current therewith, substantially asdescribed.

3. An electrical measuring instrument comprising a unilaterallyconductive solid, calibrated indicating devices 0 erable by small directcurrents connecte in series therewith, and means for electricallyconnecting a source of alternating current therewith, substantially asdescribed.

4. An electrical measuring instrument comprising a mass of carborundum,calibrated indicating devices operable by small direct currents incircuit therewith, and devices for making electrical connection betweensaid circuit and a source of alternating current, substantially asdescribed.

5. An electrical measuring instrument comprising calibrated indicatingdev ces operable by small direct currents, a rect fying device incircuit therewith, and a res1stance. shunted with the rectifying device,substantially as described.

6. An electrical measuring instrument com rising calibrated indicatingdevices operab e by small direct currents, a unilateral y conductivesolid in circuit therewith, and a resistance shunted withsaidsolid,substantially as described.

7. An electrical measuring instrument com rising calibrated indicatingdevices 0 erab e by small direct currents, a'unilateral y conductivesolid in circuit therewith, and a resistance in circuit with the solidfor mod' ing its action on the indicating devices, su stantially asdescribed.

8. An electrical measuring instrument comprising calibrated indicatingdevices operable by small direct currents, a unilatera ly conductivesolid in circuit therewith, a resistance in circuit with the solid formodifying its action on the indicating devices, and a resistance shuntedwith the solid, substantially as described.

In witness whereof, I hereunto set my hand, this 4th da of Janua 1907.

EORGE PIERCE.

In presence of IRA L. FISH,

KATHARINE A. DUGAN.

